You might want to have a look at bug reports
https://bugzilla.redhat.com/show_bug.cgi?id=505837
https://bugzilla.redhat.com/show_bug.cgi?id=518377
which dealt with this issue some time ago. Module p4-clockmod does not
provide a true frequency scaling as available on systems which support
SpeedStep. It is basically considered useless and even has
disadvantages such as increasing system latency,
http://lkml.org/lkml/2006/2/25/84 .
Modern Intel CPUs will rather use the SpeedStep driver. ~C